TUTORIAL of Microwave Ngg

TUTORIAL EC7105 MICROWAVE ENGINEERING Module – 1: 1. What are microwave? Explain the characteristic features of microwaves. Explain some of the important applications of microwaves. 2. What are the high frequency limitations of conventional tubes? Explain clearly. 3. (a) Explain how h-f limitations are overcome. (b) What is the wavelength in free space of a microwave signal whose frequency is 5.2 GHz? 4. (a) What is transit time? (b) Explain with suitable sketch the operation of two-cavity Klystron amplifier. 5. Explain the following – (i) UHF, SHF and EHF frequency bands, (ii) Give the frequency range for the following letters designation S, C, X and K bands. 6. An electron is accelerated from rest through a potential difference of 1 KV. What is the electron's terminal velocity in m/s? 7. Explain how velocity modulation creates density modulation in a Klystron amplifier. How does the reflex Klystron differ from amplifier Klystron? 8. Explain with schematic diagram the operation of Reflex Klystron Oscillator. Draw Applegate diagram for the Reflex Klystron Oscillator. 9. Obtain relation between repeller voltage and frequency of operation of Reflex Klystron Oscillator. 10. Obtain relationship between accelerating voltage and repeller voltage in Reflex Klystron Oscillator. 11. (a) What are modes in Reflex Klystron oscillator? (b) Sketch output power and frequency of Klystron versus repeller voltage for Reflex Klystron. 12. Describe with suitable diagram the following Microwave (i) Travelling wave table (TWT) (ii) Magnetron. 13. Explain the working of two-cavity Klystron amplifier, while doing so, explain the concept of velocity and current modulations. 14. In three cavity Klystron amplifier what should be the resonant frequency of the intermediate cavity? Why? Discuss efficiency obtainable with two or three cavity systems. 15. Describe the working of Reflex Klystron oscillator. What is the condition on transit time of electrons in order to sustain the oscillation? 16. Describe with the help of electronic admittance spiral how the electronic tuning is obtained in a Reflex-Klystron Oscillator. Can this oscillator be used for frequency modulation? 2md vo 17. In a reflex Klystron, show that the transit time is given by tr = --------------, e Vr

where m and e are mass and charge of electron, vo is the initial velocity, Vr is the magnitude of the repeller voltage and d is the distance from the anode to the repeller. 18. A Reflex Klystron is operating at 9GHz and the mode number n is 2. Calculate the transit time in secs. 19. (a) What is a re-entrant cavity? Explain it. (b) In Reflex Klystron, the re-entrant cavity is resonant at 9 GHz. The half power frequencies are separated ? 15 MHz from the centre frequency. Calculate the loaded Q for the cavity. 20. (a) Explain with schematic diagram the operation of two-cavity Klystron amplifier. (b) Derive an expression for the efficiency of the Klystron amplifier. (c) A two-cavity Klystron amplifier has the following parameters: Vo = 1000V, Ro = 40 K ohms, Io = 25 mA, f = 3 GHz. Gap spacing in either cavity (d) = 1 mm. Spacing between the two cavities (L) = 4 cms. Effective shunt impedance, excluding beam loading (Rsh) = 3 p K ohms. Find (i) The input gap voltage to give maximum voltage (V2) (ii) The voltage gain, neglecting the beam loading in the output cavity, (iii) The efficiency of the amplifier, neglecting beam loading. (Ans: 96.5V, 8.595, 46.2%) 21. A two-cavity Klystron operates at 4.5GHz. The dc beam voltage is 10KV. Cavity gap spacing is 2mm. For a given input, the magnitude of the gap voltage is 100V. Calculate the time the electrons are in the gap, the transit angle, and the range of velocities of electrons as they leave the gap region. (Ans. 33.7 psec, 0.95 rad, 0.598x108m/s and 0.588x108 m/s). 22. Describe qualitatively the mechanism of operation of a travelling wave tube amplifier. How the oscillations are prevented in practice. 23. What is a slow wave structure? Give some typical structures, which support slow waves. 24. Explain the working of a magnetron oscillator. With the help of the Rieke diagram, discuss its performance under varying load conditions. What is the typical range of efficiencies obtainable in a magnetron? 25. How many modes of oscillations are possible in (i) 8 cavity magnetron (ii) 6 cavity magnetron? What would be the phase difference between adjacent poles for each mode? 26. What is strapping of Magnetrons? Describe the techniques used in magnetrons for mode separation and for tuning its output frequency. 27. What do you understand by terms pulling and pushing in a magnetron oscillator? What is the condition that will excite other modes in a magnetron? 28. Explain the followings: (i) Multi-cavity magnetron. (ii) Performance charts of a Magnetron (iii) RIEKE Diagram (iv) Backward Wave Oscillator (BWO) 29. What is meant by ?-mode operation in a magnetron? Describe how strapping separates the ? mode from other possible modes. 30. With the aid of a sketch, explain the operation of a backward-wave oscillator (BWO). 31. Discuss the following microwave tubes in terms of their frequency ranges, bandwidths, efficiencies, gains, power output capabilities, and applications. (a) Two-cavity Klystron.

(b) Multicavity Klystron. (c) Reflex Klystron (d) Magnetron (e) Travelling-wave tube. 32. (a) What is a magnetron? (b) Show that for a cylindrical magnetron magnetic flux density for cut-off is given by 1 Bc = -------------------- ? 8m/e Vo b(1 - a2/b2) (c) Sketch the electron paths for different values of magnetic field strength in the cylindrical magnetron. 33. Indicate the correct choice from the following (i) The two-cavity Klystron amplifier works on the principle of (a) Velocity modulation of electron beam of (b) Amplitude modulation (c) Frequency modulation (d) Phase modulation (ii) The repeller voltage of a Reflex Klystron is essentially kept negative with respect to the resonator, because this (a) Helps to avoid mode jumping (b) Satisfies the condition of oscillation (c) Protects the repeller from rapid destruction otherwise. (d) Avoids generation of AM and FM noise. (iii) Strapping is recommended in the cavity magnetron to (a) avoid mode jumping (b) avoid cathode back-heating (c) improve phase-focusing effect (d) Ensure bunching. 34. A cylindrical magnetron has the following parameters. Inner radius = 0.15m Outer radius = 0.45m Magnetic flux density = 1.2 milliwebers/m2 (a) Calculate the Hull cut off voltage (b) Determine the cut off magnetic flux density of the beam voltage is 6KV. 35. In a Reflex Klystron, increasing the coupling of the lead to resonant cavity reduces the amplitude of oscillation. Explain the mechanism involved with the aid of the admittance spiral, assuming that the repeller voltage is such as to make the electronic admittance of the gap exactly a pure negative conductance. 36. It is observed experimentally that the lowest value of repeller mode n at which oscillations start is larger the greater the coupling of the load resistance to the resonator of a reflex Klystron. Explain how this is consistent with the admittance spiral. 37. In a reflex Klystron, it will be noted that the range through which the frequency can be varied by means of the repeller voltage is greater the higher the repeller mode. Show that this result could have been predicted from the admittance spiral itself. 38. A reflex Klystron is operating at 90GHz and the mode number n is 2. Calculate the transit time. 39. In reflex Klystron, the re-entrant cavity is resonant at 9GHz. The half power frequencies are separated ? 15MHz from the centre frequency. Calculate the loaded Q for the cavity. 40. Discuss in a qualitative way the consequences of locating the attenuator in a travellingwave tube (a) Very close to the output end of the tube of TWT and

(b) Very close to the gun end of the tube of the tube. 41. What would be the effect in a travelling-wave tube of employing an attenuator that introduced a very large reflection? 42. (a) Describe qualitatively the working of a carcinotron. (b) Is the backward wave oscillator voltage tuned? Explain it. Module – 2: 1. (a) Explain the differences between microwave transistors and transferred electron devices (TEDs). (b) Spell out the following abbreviated terms: LSA, InP, and Cd Te. (c)Describe the following: (i) Gunn effect, (ii) high-field domain theory, (iii) TwoValley theory. 2. Explain the Ridley-Watkins-Hilsum theory. 3. (a) Explain qualitatively the transferred electron effect using the diagram for the band structure of GaAs. (c) Define negative differential mobility, and state the necessary conditions for transferred electron effect to occur. 4. Describe the modes of operation for Gunn diodes. 5. For a transit-time domain mode, the domain velocity is equal to the carrier drift velocity and is about 107 cm/s. Determine the drift length of the diode at a frequency of 8GHz. 6. (a) Describe how a gunn diode can be used in an oscillator circuit. (b) Describe the circuit using coaxial and waveguide cavity. 7. Spell out the following abbreviated terms. (i) IMPATT (ii) TRAPATT (iii) BARITT 8. Describe the following (a) Read diode (b) IMPATT diode 9. (a) Explain the construction and working of IMPATT diode. (b) Explain how necessary conditions are achieved for the oscillators to take place. 10. Describe the following: (c) TRAPATT diode (d) BARITT diode 11. An IMPATT diode has a drift length of 2 ?m. Calculate (i) the drift time of the carriers, and (ii) the operating frequency of the IMPATT diode. 12. Describe an oscillator circuit using IMPATT diode. Module – 3: 1. Describe the principle and mechanism of operation of rotary attenuator. 2. Describe in detail the principle and working in of a rotary phase changer. 3. Write short notes on

(e) Variable and fixed attenuators (f) E-plane tee (g) H-plane tee (h) Slotted waveguide section. 4. Describe the working of a magic tee. How impedance matching is done to realise the ideal properties of magic tee? Give important applications of it. 5. (a) What is a scattering matrix? (b) Derive the S-matrix of a lossless, ideal magic tee. 6. Describe how a magic tee can be used as a phase shifter. 7. What is a directional coupler? Explain the working of a two-hole directional coupler. Obtain the expressions directivity and coupling factor. 8. (a) What do you understand by coupling factor and directivity of directional coupler? (b) Derive the S-matrix for a loss-less reciprocal, 4-port directional coupler. 9. a) Describe the working of a Bethe-hole coupler. (b) Write the expressions for coupling and directivity for Bethe-hole coupler. 10. Explain Faraday rotation in ferrites. What is the expression for rotation per unit length? Mention its uses. 11. The input power to a 20dB attenuator is 100mW. Find the output power and the power absorbed by the attenuator. 12. A 5 dB waveguide attenuator is specified as having a VSWR of 1.2. Assuming that it is reciprocal, find its S-parameters. Module – 4: 1 (a) Write the S-matrix for an isolator. (b) Describe the working of an isolator making use of ferrites. 2. (a) Write the S-matrix for a 3-port circulator. (b) Describe the working of a three port, waveguide circulator making use of ferrites. 3 Write down the S-matrix for a 4-point circulator. Describe the working of a four-port waveguide circulator using ferrites. 4. What is a microwave circulator? Construct a four-port circulator using two magic tees and a phase shifter. Explain with suitable sketch how this circulator works. 5. Find the scattering coefficient for a matched isolator with 1dB insertion loss and 30dB isolation. Neglect any reflection. 6. The specifications of a three-port circulator are given as insertion loss as 1 dB, isolation to be 25 dB, and VSWR equal to 1.4. Characterize the isolator by its S-parameters. Module – 5: 1. What are Microwave Integrated circuits? Write applications of those. 2. Draw the electric and magnetic fields for strip line Microstrip line, slot line, and co-planner waveguide. 3. Explain in what cases Microstrip lines are used and in what cases Slot lines are used.

4. Draw the geometrical configuration of strip line and explain the variations of characteristic impedance with W/H ratio. 5. Draw the geometrical configuration of Microstrip line and explain the variations of characteristic impedance with W/H ratio.

Module – 6: 1. Explain the various methods of measuring Microwave frequencies. 2. Explain the working principle of Microwave Power Meter. 3. What are the various methods of measuring microwave power? 4. What is Network Analyser? Explain the principle of Impedance measurement using Network Analyser. 5. Explain the Method of Gain measurement of a Horn Antenna. 6. Explain the procedure for E-plan and H-plan Radiation pattern measurement of a Horn Antenna. Module – 7: 1. Draw the block diagram of a Radar System and Develop Radar Range equation. 2. Write down Radar Range equation and explain the meaning of all the parameters in the Radar Equation. 3. What are the Performance factors of Radar? 4. Draw the Block diagram of M.T.I. Radar and explain the working principle. 5. What is Blind Speed? Explain it. 6. Draw the block diagram of CW Radar and explain its working principle. 7. Draw the Block diagram of Pulse Radar and explain its working principle. 8. What is SAR? What is its application? 9. Explain the Working principle of SAR.